The Island Growth Mechanism Of The SiCGe Epilayer On SiC

SiC is a promising semiconductor with wide band gap, however its insensitivity to visible or near infrared light greatly limits its application in optoelectronics. A lattice matched SiCGe epilayer on SiC substrate may make up this disadvantage by change of its band gap with composition ratio and make SiC-based devices to meet the needs in opto-electronic applications. A method of hetero-epitaxially growing the SiCGe alloy films on SiC substrates in a hot-wall chemical vapor deposition （HWCVD） system and the effect of the growth conditions on the island growth of the SiCGe films are presented in this thesis.The main contributions in the work done for preparation of this thesis are as follows: 1. The structure and shape of the islands depend on the growth temperature greatly. The sample has less spherical islands of diamond-cubic structure and more cascading triangular islands of zinc-blende structure as increasing the growth temperature. The growth of the SiCGe films follows SK （Stranski-Krasannov） mode. When the growth temperature is high, only cascading triangular islands are observed on the surface of the epilayer, and the 2D growth layer with zinc-blende structure forming at the initial stage of the growth reaches 40 nm, which is twice of that grown at low temperature.2. When the GeH₄ flow-rate heightens under the relatively low GeH₄ flow rate, the size and density of the island increase in the initial stage of the epitaxy. The optimal growth for a high density of uniform islands occurred with 10 SCCM GeH₄, resulting in a narrow size distribution （about 30 nm diameter） and high density. Both of the islands and the 2D growth layer have face-centered cubic structure. As increase of the C₃H₈ flow-rate, the island size increases, while the island density decreases accordingly. 3. The island growth consists of 3 steps i.e. nucleation, growth and coalescence. Under a growth condition with low density of starting nucleation, new nucleation may also take place when the firstborn islands grow up.